Variable electric resistances



Nov. 10, 1964 D. B. ORAM VARIABLE ELECTRIC RESISTANCES 2 Sheets-Sheet 1 Filed April 25, 1961 m km l////+ m 2 7 2 1 4 3 n Z T a K w w 6 W 3 3 y K MNA ATTORNEYj Nov. 10, 1964 D. B. ORAM 3,156,890

VARIABLE ELECTRIC RESISTANCES Filed April 25, 1961 2 Sheets-Sheet 2 Arm/elven United States Patent 3,156,890 VARIABLE ELECTRIC RESISTANCES Daphne Blake Gram, Wrotham, England, assignor to Reliance Controls Limited, a Eritish company Filed Apr. 25, 1%1, Eer. No. 105,433 Claims priority, application Great Britain May 3, 1966 15 Claims. (Cl. 338-174) The present invention relates to variable electric resistors and specifically to variable electric resistors of the type comprising a resistive element formed by a singlelayer winding of wire on an elongated core of electricallyinsulating material, and having a wiper adapted for movement over and in contact with the turns of wire on the core.

According to the present invention, in a variable electric resistor of the type specified the elongated core carrying the winding of wire is wound into a spiral with an elongated, insulating strip interleaving the turns of the spiral, one edge of the strip being elevated above the corresponding edge of the spirally-wound core to define a spiral channel constituting a guide for the wiper which is adapted to make contact with the edge of the winding in the channel. Preferably the spiral is fiat.

The wiper preferably comprises an elongated resilient metal member of which at least a part is of U-shape, and a fixed slip-ring is provided with an annular groove in a cylindrical surface thereof, the slip ring being coaxial with the spiral-shaped resistance element and the limbs of the U-shaped member engaging the groove and clasping the slip ring. The actual contact between the wiper and the resistance element can be made by a contact member carried by the U-shaped member but preferably the end of one limb of the U-shaped member is formed into a suitable contact. As the wiper contact progresses along the spiral channel the U-shaped member clasping the slip ring rotates around the slip ring and at the same time slides in a direction parallel to the arms of the U.

The invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a potentiometer,

FIG. 2 is a plan View of the same potentiometer along the line 2-2 of FIG. 1, and

FIG. 3 is a view of part of the potentiometer partly broken away in the direction indicated by the arrow Y in FIG. 2. Like parts in the drawings have the same reference.

Referring to FIG. 1 a former or boss 1 of elect insulating material is mounted on which is in turn mounted on a base ricallya bearing housing 2 interleaving strip 5 composed of electrically-insulating material. The resistance element 4 is formed by winding successive turns of wire on an elongated core composed of electrically-insulating material.

The edge 6 of the strip 5 is elevated above the edge 7 of the resistance element and hence a spiral channel 8 is formed between adjacent convolutions of the strip 5.

The resistance element 4 and the strip 5 rest on a recessed insulating support plate 9 which is held against a shoulder 10 of the former 1 by an insulating base plate 11. In the cavity thus formed between the base plate 11 and the support plate 9 is a tapping element 12 which is resiliently biased into engagement with the resistance-element 4 at a predetermined part of the element 4. The tapping element 12 is used to obtain a tapping from the resistance element 4, the tapping element 12 being connected, if desired, to an external circuit by way of the conductor W.

Referring now to FIG. 2 a shaft 14 is rotatably mounted in bearings carried in the bearing housing 2 (FIG. 1)

and carries an arm 15 secured to the shaft 14 by means of a bolt 16. The end of the arm 15 furthest from the shaft 14 carries a bell-cranked arm 17 pivotally mounted on the arm 15 at a pivot point 18. The arm 17 is formed with a sleeve 1% through which an end part of a wiper 20 is passed, the wiper 20 being formed with a U-shaped part 21 the limbs of which slidably engage a groove 22 (FIG. 1) in the cylindrical surface of a slip ring 22. The part of the wiper 2!? which passes through the sleeve 19 extends downwardly to make electrical contact with the resistance element 4 in the groove 8 with contact portion 23 of the Wiper 20. The wiper 20 is resiliently biased into engagement with the resistance element 4 by means of a leaf spring 24 rigidly fixed to the bell cranked arm 17 by means of a clamp 17.

As the arm 15 is caused to rotate with the shaft 14 about the axis of the spiral formed by the resistance element 4, the contact portion 23 of the wiper 20 is caused to progress along the channel 8 and the bell-cranked arm 17 is simultaneously caused to rock about its pivot point 18. The limbs of the U-shaped part 21 of the wiper 20 slide relative to the slip ring 22' in a direction parallel to the limbs as the wiper 2t) traverses the channel 8 and thus electrical contact between the wiper 20 and the slip ring 22' is maintained despite variations in the radial distance of the contact portion 23 of the wiper 20 from the axis of the resistance element 4.

When the contact portion 23 of the wiper 29 has reached the limit of its path which is furthest from the axis of the resistance element 4 the bell-cranked arm 1'7 abuts an abutment 25 on a ring 27 (not visible in FIG. 2). Conversely when at the limit of its path nearest the axis of the resistance element 4 the bell-cranked arm 17 abuts an abutment 26 on a ring 28.

The successive positions of the arm 15 and the bellcranked arm 17 shown in dash-dot lines at 17 and 17 are the positions assumed when the contact portion 23 of the wiper 20 is in the halfway position along the channel 8 and in the position furthest from the axis of the resistance element 4 respectively. The full-line position of the bell-cranked arm 17 is the position in which the contact portion 23 is nearest the axis of the spiral.

In FIG. 3 the contact portion 23 is shown to have a radius at its point of contact and it can be seen that the bell-cranked arm 17 at its end 34 remote from the wiper contact portion 23 is upturned and then turned horizontally back to the pivot 18. The end 29 of the bell-cranked arm 17 carrying the wiper portion 23 is bent downwardly. The parts 29 and 34 of the bell-cranked arm 17 abut the abutments 25 and 26 respectively at the two limits of travel.

The abutments 25 and 26 are circumferentially spaced apart by such an amount that the wiper 2t) completes an integral number of turns when it progresses from one end of the wound element 4 to the other.

Referring again to FIG. 1 the conductor 13 within the insulated jacket 30 is used to connect the slip ring 22 to an external circuit while the two ends of the resistance element 4 are also connected to an external circuit by conductors (not shown) extending through an enclosing cylindrical shell 31. The shell 31 also supports the rings 27 and 28 on a shoulder 32 against which they are held by an end plate 33.

When it is desired to make a potentiometer which has a linear relationship between the change of resistance presented to an external circuit and the angular displacement of the shaft 14, the element is preferably as produced by the machine as described in copending patent application No. 105,353 filed April 25, 1961. Such application describes a machine for winding a spiral resistance element comprising a coiling head for coiling an elongated flexible insulating core into a spiral, a guide adapted to guide the elongated core through a winding head to the coiling head and having an outlet mouth adjacent the coiling head, the winding head being adapted to wind wire about the core as it passes from the outlet mouth of the guide to the coiling head, and means for moving the guide and winding head in dependence upon the progressive increase in the diameter of the spiral in such a manner that the mouth of the guide moves substantially along a line radial of the centre of the spiral and that the length of core tangential to the spiral and extending to the mouth of the guide subtends a substantially constant angle at the centre of the spiral.

What is claimed is:

1. A variable electric resistor comprising, in combina tion, an elongated core of electrically insulating material, a resistance wire element would about said core, a wiper structure contacting the edge of the resistance wire, such wire-wound core being further wound into a substantially flat spiral, and an elongated insulating strip interleaved between the turns of said spiral having one edge of said strip standing elevated above the correspond ing edge of the spirally-wound core to define a spiral channel which constitutes a guide for said wiper element, said wiper structure including an elongated resilient metal member of which at least a part is of substantially U- shape, and a fixed slip ring provided with an annular groove in a cylindrical surface thereof, the slip ring being substantially coaxial with the spiral-shaped resistance element and the limbs of the U-shaped member engaging the groove and clasping the slip ring.

2. A variable electric resistor comprising, in combination, an elongated core of electrically-insulating material, a resistance wire element wound about said core, a wiper element contacting the edge of the resistance wire, such wire-wound core being further wound into a spiral, an elongated insulating strip interleaved between the turns of said spiral having one edge of said strip standing elevated above the corresponding edge of the spirally-wound core to define a spiral channel which constitutes a guide for said wiper element, a bell-cranked arm pivotally mounted on the end of a further arm which is, in turn, pivotally mounted at the axis or" the resistance element, and abutments determining the limiting positions of the contact portion of said wiper and adapted to abut the ends respectively of said bell-cranked arm when the contact portion is at its limiting positions respectively.

3. A variable electric resistor according to claim 2 wherein said bell-cranked arm is pivotally mounted at its centre on the further arm.

4. A variable electric resistor according to claim 2 wherein one end of said bell-cranked arm is substantially coincident with the contact portion of the wiper.

5. A variable electric resistor according to claim 2 wherein the limiting positions are such that the contact portion of the wiper completes an integral number of convolutions in progressing from one limiting position to the other.

6. A variable electric resistor, comprising a resistance element of spiral form, a rotatable shaft, an annularlygrooved cylindrical slip ring coaxial with said shaft, and a wiper coupled to said shaft for rotation therewith, said wiper having a U-shaped body of resilient metal wire the limbs of which engage the groove in said slip ring and clasp said slip ring and a contact portion engaging the resistance element during travel along substantially the entire spiral form therof.

7. A variable electric resistor, comprising a resistance element of spiral form, a rotatable shaft coaxial with said element of spiral form, a first arm mounted on said shaft for rotation therewith, said first arm extending radially from said shaft, a second arm pivotally mounted intermediate its ends on the end of said first arm remote from said shaft, 21 wiper mounted for movement by said first arm over and in contact with said resistance element, and two abutment members to abut the ends respectively of said second arm to determine two limiting positions respectively of said wiper.

8. A variable electric resistor as claimed in claim 7, wherein said first arm is pivotally mounted at its center on said second arm.

9. A variable electric resistor as claimed in claim 7,

wherein said second arm is cranked at the point where it is pivotally mounted on said first arm.

10. A variable electric resistor as claimed in claim 7, wherein said two limiting positions define a traversal of an integral number of convolutions of said resistance element by said wiper.

11. A variable electric resistor comprising an elongated core of electrically-insulating material, a single layer winding of wire on said core, saidcore carrying said Windinghaving a spiral form, an elongated strip of electrically-insulating material interleaving the convolutions of said core of spiral form, one edge of said interleaving strip standing elevated above the corresponding edge of said core to define a guide channel, a rotatable shaft, a first arm mounted on said shaft for rotation therewith, said first arm extending radially from said shaft, a second arm pivotally mounted intermediate its ends on the end of said first arm remote from said shaft, an annually grooved cylindrical slip ring coaxial with said shaft, a Wiper having a U-shaped body of resilient metal wire the limbs of which engage the groove in said slip ring and clasp said slip ring, said wiper being coupled to said second arm for movement, on rotation of said shaft, along said channel in contact with the edge of said winding in said channel, and two abutment members to abut the ends respectively of said second arm and to determine two. limiting positions respectively of said wiper.

12. A variable electric resistor, comprising an elongated core of electrically-insulating material, a singlelayer winding of wire on said core, said core carrying said winding having a spiral form, an elongated strip of electrically-insulating material interleaving the convolutions of said core of spiral form, one edge of said interleaving strip extending beyond the corresponding edge of said core to denne a guide channel, a rotatable shaft, an annularly grooved cylindrical slip ring coaxial with said shaft and a wiper having a U-shaped body of resilient metal wire the limbs of which engage the groove in said slip ring and clasp said slip ring, said wiper being coupled to said shaft for rotation therewith and for movement along said channel in a direction approximately perpendicularly to the axis of said shaft and in contact with the edge of said winding in said channel.

13. A variable electric resistor, comprising a resistance element of spiral form, a rotatable shaft, a first arm mounted on said shaft for rotation therewith, said first arm extending radially from said shaft, a second arm pivotally mounted intermediate its ends on the end of said first arm remote from said shaft, an annularly grooved cylindrical slip ring coaxial with said shaft, a wiper having a U-shaped body of resilient metal wire the limbs of which engage the groove in said slip ring and clasp said slip ring, said wiper being coupled to said second arm for movement, on rotation of said shaft, in contact with said resistance element, and two abutment members to abut the ends respectively of said second arm and to determine two limiting positions respectively of said wiper.

14. A variable electric resistor, comprising a resistance element of substantially spiral form, a rotatable shaft, a grooved cyldindrical slip ring on said shaft, and wiper means coupled to said shaft for rotation therewith and operable to move relative to said slip ring in a direction approximately perpendicularly to the axis of said shaft, said Wiper means including a substantially U-shaped body of resilient conductive material with the limbs thereof engaging the groove in said slip ring and clasping said slip ring and a contact engaging portion electrically connected with one of said limbs and operable to displace said limbs in said groove during movement thereof along the spiral form of said resistance element.

15. A variable electric resistor, comprising an elongated core of electrically-insulating material, a winding of wire on said core, said core carrying said winding having a substantially spiral form, a strip of electrically-insulating material interleaving the convolutions of said core of spiral form, one edge of said interleaving strip extending beyond the corresponding edge of said core to define a guide channel, a rotatable shaft, a grooved slip ring on said shaft, wiper means including a substantially U-shaped body of resilient conductive material with the limbs thereof engaging the groove in said slip ring and clasping said 15 slip ring, means operatively connecting said wiper means to said shaft for rotation therewith, and means including a contact engaging portion operable to engage said winding Within said channel for displacing said limbs within said groove relative to said shaft by the effective radial movements of said contact engaging portion along the spirally-shaped channel.

References Cited in the file of this patent UNITED STATES PATENTS 1,785,779 Lauter Dec. 23, 1930 2,090,347 Draving et al. Aug. 17, 1937 2,429,592 Beagles Oct. 28, 1947 2,578,353 Hampton et a1 Dec. 11, 1951 2,853,586 Vercesi Sept. 23, 1958 

12. A VARIABLE ELECTRIC RESISTOR, COMPRISING AN ELONGATED CORE OF ELECTRICALLY-INSULATING MATERIAL, A SINGLELAYER WINDING OF WIRE ON SAID CORE, SAID CORE CARRYING SAID WINDING HAVING A SPIRAL FORM, AN ELONGATED STRIP OF ELECTRICALLY-INSULATING MATERIAL INTERLEAVING THE CONVOLUTIONS OF SAID CORE OF SPIRAL FORM, ONE EDGE OF SAID INTERLEAVING STRIP EXTENDING BEYOND THE CORRESPONDING EDGE OF SAID CORE TO DEFINE A GUIDE CHANNEL, A ROTATABLE SHAFT, AN ANNULARLY GROOVED CYLINDRICAL SLIP RING COAXIAL WITH SAID SHAFT AND A WIPER HAVING A U-SHAPED BODY OF RESILIENT METAL WIRE THE LIMBS OF WHICH ENGAGE THE GROOVE IN SAID SLIP RING AND CLASP SAID SLIP RING, SAID WIPER BEING COUPLED TO SAID SHAFT FOR ROTATION THEREWITH AND FOR MOVEMENT ALONG SAID CHANNEL IN A DIRECTION APPROXIMATELY PERPENDICULARLY TO THE AXIS OF SAID SHAFT AND IN CONTACT WITH THE EDGE OF SAID WINDING IN SAID CHANNEL. 